Offense totally laid an egg.
Going by your standard where average is not good enough any game where BYU scored less than 24 points should be considered a failure on part of the offense.
Just for clarification the average for scoring is actually 27 ppg but I will use 24 because we get less possessions because of the style of the defense.
I am also only including games where the offense scored less than 24 and the defense held the other team to 24 or less.
2016 - 2 games utah and ucla - 11 wins
2017 - Utah Boise Fresno and umass - 8 wins, maybe 9 with a bowl game
2018 - cal niu Boise - 10 wins
2019 - SDSU - 8 wins
2020 - coastal Carolina - 12 wins
2021 - no games because the defense was clearly inferior
Also, going by what you said if you defend the offense you are defending mediocrity.